This invention deals with the measurement of gas cut or gas holdup in multiphase fluid flow in a cased well borehole. More particularly, this instrument deals with an apparatus for measuring the volume of gas present in a multiphase flow regime in a cased oil or gas well borehole.
The problem long existing in the area of production logging of cased well boreholes has been to separate the phases of flow, namely solid, liquid or gaseous, and measure each component of the multiphase flow. Addition of the phases of solid, liquid, and gas in a multiphase flow provides the totals. The liquid phase may also contain slugs of oil or water interspersed with the solid particles and the gaseous phase may be in the form of small bubbles or large bubbles. So called stratified flow may occur at locations where the well casing may be horizontal or nearly horizontal or where the gas phase has separated by gravity from the liquid and solid phase and formed a stratified gaseous layer.
Of course, the measurement of the liquid phase, solid phase, and gaseous phase of the well fluid may be divided into separate measurements of each of the phases. The present invention concerns instruments and techniques for measuring the gaseous phase of fluid flow in a cased well borehole in which the gaseous phase is separated out, i.e., not in solution, from the liquid phase in the form of small or large gas bubbles or stratified fluid flow. The techniques and apparatus of the present invention are not believed to be applicable in the situation where the gas produced by the well is in solution with the liquid phase. However, as will be discussed in more detail subsequently, the present apparatus and techniques do encompass methods for the measurement of gas holdup or percentage volume gas flow in either bubble form or stratified form of flow in the cased well borehole.